Final answer:
A backup path that is guaranteed to be loop-free in EIGRP is called a Feasible Successor.
Step-by-step explanation:
In EIGRP, a backup path that is guaranteed to be loop-free is called a Feasible Successor.
In EIGRP (Enhanced Interior Gateway Routing Protocol), a backup path that is guaranteed to be loop-free is referred to as a "feasible successor." EIGRP employs the concept of feasible successors to provide a mechanism for fast and loop-free convergence in the event of a primary path failure.
Feasible successors are alternative routes to a destination network that meet the feasibility condition, ensuring that they have an advertised metric (computed distance) less than the metric of the current successor path. If the primary path fails, EIGRP can quickly transition to a feasible successor without the need for the recomputation of the entire topology table, reducing convergence time.
This loop-free backup path allows EIGRP to maintain network stability and reliability by offering a pre-validated alternative route to a destination, enhancing the protocol's ability to recover efficiently from link or node failures in a network.